The invention described herein arose in the course of, or under, Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.
This invention relates to an insulated tube for a laser and a method of making same. More particularly, this invention relates to an insulated laser tube with a particular insulation structure and a method of making this particular insulation structure.
In the operation of a laser, and more particularly in the transport of the laser beam from the source to the target, it is critical to the performance of the laser that the evacuated enclosure, such as a tube, through which the laser passes be maintained at a constant temperature. Furthermore, when very high temperatures are used, i.e., temperatures of over 1000.degree. C., and in some instance in excess of 1500.degree. C., the use of ceramic materials is dictated by the temperature. It is important to the life of the ceramic tube that temperature gradients along the length of the tube, and resultant stresses, be avoided, i.e., that the temperature be uniform along the entire length of the tube. This, in turn, requires a highly insulated structure.
Prior art approaches to this problem have included the use of prefabricated tubular bats of fibrous insulation which are placed around the laser tube to be insulated. In some instances, an outer shell, e.g., a quartz tube is then placed around the fibrous insulation, not only to secure it in place, but also to provide mechanical or structural protection to the insulation.
However, it has been found that such prefabricated tubular insulation, when assembled around the ceramic laser tube at room temperature, prior to heating the laser tube to operating temperature, results in a structure wherein voids are present between the outer wall of the ceramic laser tube and the inner surface of the prefabricated tubular fibrous insulation. Such voids, being non-homogeneous in size and position, result in varying degrees of insulation value at various positions along the ceramic laser tube resulting, in turn, in temperature variations along the laser tube. Ideal laser performance will be achieved if the temperature gradients throughout the laser are less than about 25.degree. C. Large temperature variations degrade the performance of the laser, and also are sufficient to eventually cause damage to the ceramic laser tube due to the resultant thermal stresses set up in the ceramic tube by such thermal gradients, particularly at operating temperatures in excess of 1500.degree. C.
It would, therefore, be desirable to provide an insulated ceramic laser tube having a more uniform high temperature insulation surrounding the walls of the tube and a method of forming such uniform insulation.